1. Field of Invention
Present invention is a new and useful process directed to forming a block copolymer. The process is directed to forming a block copolymer of two different amide polymers, having utility, for example, after additional processing, as a fiber. The copolymer comprises blocks of monomeric repeating units of each of the two different amide polymers. One of the amide polymers is a polyetheramide and the other is a polylactam which is inherently ether free. By way of comparison, a copolymer can comprise random sequences of repeating units of each of the aforementioned polymers. The latter is often referred to as a random copolymer. As is known, a block copolymer and a random copolymer formed from the same two compounds will possess different properties.
2. Description of the Prior Art
Melt blending is a generally known method for preparing block copolymer comprising amide polymers. It comprises mixing the two different amide polymers, heating the mixture to a temperature above at least one of the amide polymer's melting point, but below any decomposition temperature and blending the heated polymers at a temperature until a block copolymer is formed. The heating then is stopped and the copolymer is allowed to cool. Such a method is described in U.S. Pat. Nos. 4,136,133, 4,130,602, 4,113,794 and 4,168,602. The information contained in the aforementioned patents is incorporated herein by reference.
Other methods of preparing block copolymers are disclosed in U.S. Pat. Nos. 4,044,071 and 4,045,511, which information is also incorporated herein by reference. In the latter two patents, a block copolymer is prepared by mixing a polyamide (ether-free) and a salt of a prepolyetheramide, heating the mixture at a suitable temperature until the salt polymerizes and the resulting polymer forms blocks with the polyamide.
However, applicant has found that, contrary to one's expectation that a random copolymer would be formed by heating a mixture of a lactam and a polyetheramide, a block copolymer is indeed formed. The expectation of a random copolymer is based on the concept that when e.g., the caprolactam starts to form short chains, amide interchange between the short chains and polyetheramide would occur and form a random structure rather than a block structure.